Xenotransplantation of human unrestricted somatic stem cells in a pig model of acute myocardial infarction.

BACKGROUND: Stem cell therapy may help restore cardiac function after acute myocardial infarction (AMI), but the optimal therapeutic cell type has not been identified. METHODS: We examined the effects of CD34-/CD45- human unrestricted somatic stem cells (USSCs) in pigs (n = 30) with an AMI created by a 90-min occlusion of the left anterior descending coronary artery. Pigs were randomly assigned to receive either USSCs (302 ± 23 × 10(6) cells) or phosphate-buffered saline via 15 NOGA-guided transendocardial injections 10 days after AMI. Cyclosporine A (10 mg/kg orally, twice a day) was started in all pigs 3 days before control or cell treatment. Cardiac function was assessed by echocardiography before injection and at 4 and 8 weeks after treatment. Serum titers for pig IgG antibodies against USSCs were also measured at these time points and before AMI. RESULTS: Compared with control pigs, USSC-treated pigs showed no significant differences in any of the functional parameters examined. USSC-treated pigs showed variable increases in anti-USSC IgG antibody titers in the blood and chronic inflammatory infiltrates at the cell injection sites. Immunohistochemical studies of the injection sites using human anti-mitochondrial antibodies failed to detect implanted USSCs. CONCLUSIONS: We conclude that human USSCs did not improve cardiac function in a pig model of AMI. Cell transplantation in a xenogeneic setting may obscure the benefits of stem cell therapy.

Human hepatocyte growth factor (VM202) gene therapy via transendocardial injection in a pig model of chronic myocardial ischemia.

BACKGROUND: Hepatocyte growth factor (HGF) may stimulate angiogenesis. We examined the safety and therapeutic potential of the HGF plasmid (VM202) in pigs with chronic myocardial ischemia. METHODS AND RESULTS: We delivered VM202 or vehicle transendocardially to 4 groups of pigs: vehicle control (n = 9); high-dose VM202 (n = 9); low-dose VM202 (n = 3); and normal control (no ischemia; n = 1). Pigs were killed 3, 30, and 60 days after injection. No adverse events were associated with VM202 treatment or delivery. Quantitative polymerase chain reaction indicated that heart injection sites had the highest levels of VM202 (day 3), which became almost undetectable by 30-60 days. Most nontarget tissues showed clearance of VM202 plasmid by day 30. Control and VM202-treated pigs did not differ in global functional data. Dobutamine-stressed myocardial-contrast echocardiogram suggested that VM202 may help preserve microvascular perfusion at 30 days; reperfusion velocity in ischemic myocardium decreased significantly in control (baseline to follow-up, 5.1 ± 1.9 to 2.7 ± 1.0; P = .031) but not in VM202 groups (high-dose: 3.1 ± 1.1 vs 3.1 ± 1.5 [P = .511]; low-dose: 3.8 ± 1.1 vs 3.9 ± 1.5 [P = .559]). Linear local shortening increased significantly from day 0 to 30 in VM202-treated versus control pigs (5.0 ± 4.7% vs 9.2 ± 7.5% vs 0.9 ± 5.8% [high-dose, low-dose, control, respectively]; P = .021). CONCLUSIONS: Transendocardial delivery of VM202 was safe and may help to preserve microcirculatory perfusion and improve wall motion.

Comparative healing response after sirolimus- and paclitaxel-eluting stent implantation in a pig model of restenosis.

OBJECTIVE: We compared local vessel healing and inflammatory responses associated with nonoverlapping sirolimus-eluting stents (SES) and paclitaxel-eluting stents (PES). BACKGROUND: Sirolimus and paclitaxel may have different effects on vascular healing. In the present study, we analyzed the local histologic effects of drug-eluting stents (DES). METHODS: We placed 43 stents (22 PES and 21 SES) in 16 Yucatan minipigs. Stents were randomly assigned and placed in the left anterior descending, circumflex, or right coronary arteries (one stent per artery), covering a region previously injured by balloon angioplasty. RESULTS: Histopathologic analysis showed that the distribution of injury scores was similar between the two stent groups, reflecting the homogeneity of coronary injury secondary to balloon overstretch. Electron microscopy showed complete endothelialization in most cases. Incomplete endothelialization was present in 12.5% of PES and almost 20% of SES at 30 days. In the PES group, moderate to severe inflammation was found in eight arteries, whereas only one vessel had moderate inflammation in the SES group. Severe inflammation was observed significantly more often in the PES than in the sirolimus group (P = 0.006). With the PES group, stent struts overlying side branches had a significantly higher frequency of poor endothelialization scores than did stent struts that did not overlay side branches (P = 0.006). CONCLUSIONS: In this preclinical study in a pig model of in-stent restenosis, implantation of nonoverlapping DES was associated with local inflammatory reactions and decreased endothelial repair. Impaired endothelialization was visualized in the struts overlying side branches.

Validation of QwikStar Catheter for left ventricular electromechanical mapping with NOGA XP system.

Left ventricular electromechanical mapping (LVEM) is a method for mapping the left ventricular cavity in 3 dimensions by use of a catheter that samples points on the endocardial surface. These points provide data on unipolar voltage and linear local shortening, which can then be used to evaluate myocardial ischemia and viability. The new QwikStar multi-electrode catheter, which acquires data from multiple points simultaneously, potentially improves map quality and decreases mapping time in comparison with the single-point NogaStar catheter. Our study sought to validate the QwikStar catheter's LVEM capabilities in a porcine model of chronic ischemia.Eight pigs underwent ameroid placement over the proximal left circumflex artery, to induce chronic ischemia. In 60 days, LVEM was performed on each animal with the NogaStar and QwikStar catheters. Unipolar voltage and linear local shortening results were displayed in 9-segment polar maps. The unipolar voltage data from both maps were then correlated by means of linear regression.There were no adverse events during LVEM. Mapping time was similar for both groups (QwikStar, 44.6 +/- 25.62 min; NogaStar, 65.75 +/- 25.33 min; P = 0.13). Results of mean unipolar voltage maps acquired with the 2 catheters showed a moderate correlation (r =0.59, P <0.001). Selecting segments with more than 6 point samples increased the Pearson coefficient to 0.69 (P <0.001).Our findings show that the QwikStar catheter enables the reproducible performance of LVEM by sampling fewer points, which shortens procedure time, decreases manipulation of the left ventricular cavity, and might increase procedural safety.

Histopathological validation of electromechanical mapping in assessing myocardial viability in a porcine model of chronic ischemia.

BACKGROUND AND OBJECTIVE: Left ventricular electromechanical mapping (EMM) determines myocardial viability on the basis of endocardial electrograms. The aim of the present study was to validate EMM in differentiating infarcted myocardium from viable myocardium by histopathological analysis. METHODS: Sixty days after implanting an ameroid constrictor over the left circumflex artery to create chronic ischemia in 19 pigs, EMM was performed to construct unipolar voltage (UPV), bipolar voltage (BPV) and linear local shortening (LLS) maps. Noninfarcted and infarcted myocardium were identified by histopathology. Threshold determinations comparing noninfarcted tissue with scarred tissue were made by measuring the area under the receiver operating characteristic curves. RESULTS: From the 19 hearts, 149 myocardial segments were divided into noninfarcted myocardium (n=128) and transmural infarct (n=21). UPV, BPV and LLS values (4.7+/-1.2 mV, 2.8+/-2.5 mV and 10.0+/-5.1%, respectively) of infarcted segments were significantly lower than those in noninfarcted myocardium (10.9+/-3.4 mV, 4.5+/-2.4 mV and 15.7+/-9.5%, respectively; P<0.01 for each comparison). The threshold values of UPV, BPV and LLS differentiating noninfarcted from infarcted myocardium were 6.2 mV (98% sensitivity, 95% specificity, 97% accuracy), 2.8 mV (80% sensitivity, 72% specificity, 79% accuracy) and 12.3% (68% sensitivity, 67% specificity, 68% accuracy), respectively. The relative dispersion of voltage was lower for UPV versus BPV. CONCLUSION: UPV can accurately differentiate infarcted from noninfarcted tissue in the chronic ischemic heart of pigs; however, BPV and LLS results were less accurate.

Imaging long-term fate of intramyocardially implanted mesenchymal stem cells in a porcine myocardial infarction model.

The long-term fate of stem cells after intramyocardial delivery is unknown. We used noninvasive, repetitive PET/CT imaging with [(18)F]FEAU to monitor the long-term (up to 5 months) spatial-temporal dynamics of MSCs retrovirally transduced with the sr39HSV1-tk gene (sr39HSV1-tk-MSC) and implanted intramyocardially in pigs with induced acute myocardial infarction. Repetitive [(18)F]FEAU PET/CT revealed a biphasic pattern of sr39HSV1-tk-MSC dynamics; cell proliferation peaked at 33-35 days after injection, in periinfarct regions and the major cardiac lymphatic vessels and lymph nodes. The sr39HSV1-tk-MSC-associated [(18)F]FEAU signals gradually decreased thereafter. Cardiac lymphography studies using PG-Gd-NIRF813 contrast for MRI and near-infrared fluorescence imaging showed rapid clearance of the contrast from the site of intramyocardial injection through the subepicardial lymphatic network into the lymphatic vessels and periaortic lymph nodes. Immunohistochemical analysis of cardiac tissue obtained at 35 and 150 days demonstrated several types of sr39HSV1-tk expressing cells, including fibro-myoblasts, lymphovascular cells, and microvascular and arterial endothelium. In summary, this study demonstrated the feasibility and sensitivity of [(18)F]FEAU PET/CT imaging for long-term, in-vivo monitoring (up to 5 months) of the fate of intramyocardially injected sr39HSV1-tk-MSC cells. Intramyocardially transplanted MSCs appear to integrate into the lymphatic endothelium and may help improve myocardial lymphatic system function after MI.

Hemostatic control of coronary arteries with poloxamer 407 reverse-thermal polymer during off-pump coronary artery bypass surgery in a pig model.

OBJECTIVE: : To evaluate a new material, poloxamer 407 reverse-thermal polymer, which may be of value in controlling bleeding during off-pump coronary anastomoses. METHODS: : Poloxamer 407 reverse-thermal polymer is a clear, nontoxic compound that is a viscous liquid at room temperature but instantly changes to a firm, water-soluble gel when warmed to body temperature. Six pigs underwent off-pump coronary artery bypass with the left internal mammary artery to the left anterior descending coronary artery. Blood loss from the arteriotomy was measured over a 15-minute period before and after injection of 500 µL intracoronary polymer. After completion of the anastomosis, 10 mL of cold saline was poured along the left anterior descending artery to facilitate dissolution of the polymer. The heart was allowed to beat 2 additional hours with blood flowing through the left internal mammary to left anterior descending graft, after which a completion angiogram was obtained to evaluate graft patency and to look for gross angiographic evidence of coronary branch occlusion or intraluminal filling defects. The animals were then humanely euthanized, and myocardium from the area subtended by the left anterior descending was harvested for histologic evaluation. RESULTS: : All animals successfully underwent the surgical procedure and survived until study termination without any complications. The amount of bleeding from coronary arteriotomy was significantly higher before intracoronary injection of the polymer (5.25 ± 1.65 mL/min versus 0.54 ± 0.53 mL/min, P = 0.0004). Angiography demonstrated that the graft was patent, and there was no evidence of intraluminal foreign bodies. Myocardial samples from the subtended bed showed no evidence of intraarterial polymer or myonecrosis. CONCLUSIONS: : Poloxamer 407 reverse-thermal polymer may be a valuable tool in performing coronary anastomoses off-pump. Completion angiograms showed total dissolution of the material with no residual intraarterial polymer visible on tissue samples.